This invention relates to fire-fighter training. In particular, the invention relates to fire-fighter training installations such as those used to simulate fires in aviation scenarios, notably those of aircraft crash-landings.
The invention is not limited to aviation fire-fighting scenarios: it has application in simulators for other fire-fighting scenarios such as road or railway crashes that, like an aircraft crash-landing, can involve a substantial fuel spill. Indeed, preferred aspects of the invention involve simulators that can be adapted for a variety of different fire simulations not necessarily involving fuel spillage, including aircraft, collapsed buildings, road-vehicles, trains and multiple-scenario incidents. Such simulators can also be used for ‘joint services’ training, i.e. to train members of other emergency services, notably the police and paramedics, who must co-ordinate their work with fire-fighters from time to time.
Speed and skill are of the essence to all fire-fighters but fire-fighting in aviation scenarios, such as aircraft crash-landings, requires particularly fast response and skilled teamwork if loss of life is to be minimised. It is generally accepted that unless a burning crash-landed aircraft is accessed and the fire suppressed within two minutes of ignition, there is little hope of survival for those on board who may have survived the landing itself. As there is so little time for mistakes, this places extraordinary demands upon the skill of fire-fighters based at civil airports and military airbases. There are corresponding demands upon the training of those fire-fighters, both as individuals and as a team, and hence upon the quality of the simulators on which those fire-fighters practice.
All substantial airports and airbases have dedicated fire tenders on standby for substantially immediate high-speed access to any crash site within the airport or airbase perimeter. Such tenders include vehicles known in the art as Major Airport Crashtrucks or MACs. Upon approaching the stricken aircraft, the practice is to drive the tenders close to the aircraft for the purpose of laying down fire-retardant foam and simultaneously gaining access to the fuselage of the aircraft to free its passengers and crew. Indeed, recent practice in civil aviation fire-fighting is to drive a specially-adapted tender right up to the aircraft for the purposes of puncturing its fuselage and injecting foam to protect people who may still be alive within.
Of course, accidents are characterised by their unpredictability and there is no way of knowing what difficulties fire-fighters will encounter when they reach a crash-landed aircraft. Their fire-fighting strategy must therefore be fully flexible. For example, the orientation of a burning aircraft with respect to the prevailing wind will have a considerable influence upon how the fire-fighters can approach the aircraft, suppress the fire and access the fuselage. Also, obstructions such as airport vehicles and broken-off engines, undercarriage components, wings or other parts of the aircraft can block access to the fuselage and will, in all likelihood, be on fire themselves. This is all quite apart from the different types of aircraft fire with which fire-fighters must contend: a fire confined to an engine or the undercarriage, for example, will require a quite different strategy to a fire involving spilled fuel.
The demands of fire-fighter training have led to the emergence of fire-fighting simulators in which fluid-fuelled flames are controlled to respond realistically to efforts by trainees to suppress them, in so-called ‘hot-fire’ training. Aviation fire simulators are typically sited at an airfield or airbase, close to the fire-fighters' base at that facility. Flame generators can extend across the ground to simulate a fuel spill and can also be associated with mock-ups of above-ground structures associated with a fire scenario, such as a metal tube representing a section of aircraft fuselage which may have structures representing wings and engines to one or both sides, or a metal box representing an airport vehicle. In an analogy apt for acting-out scenarios, these mock-ups are referred to in fire-fighter training as ‘props’. That term will be used hereafter in this specification when referring to such mock-ups.
In early days, the fuel used in aviation fire simulators was liquid fuel such as oil or jet fuel but whilst their flames are realistic in appearance, those fuels give rise to levels of pollution that would be unacceptable today in frequently-used simulators that are often situated near urban settlements. Consequently, there has been a move toward gas-fuelled simulators and here the challenge is to maintain realism and controllability.
The aim of any fire simulator is to mimic the behaviour of a flame as it develops from ignition to eventual extinction. Spilled liquid fuel burns in a similar manner to the same fuel in an open-topped tank. Upon ignition, the height of the flames is initially quite small. However, the flames progressively grow larger and spread quickly across the full area of the spillage, eventually reaching a limiting height determined by the burning velocity of the flame. The flame grows during this phase because its radiant heat promotes the evaporation of liquid fuel. The increased rate of evaporation causes the flame to grow and this applies additional radiant heat to the remaining liquid fuel, increasing the rate of evaporation still further until the burning velocity of the flame prevents further flame growth.
Reference is made at this point to FIG. 1, whose source is Drysdale, D. An Introduction to Fire Dynamics, 2nd edition, p. 12, published in 1998 by John Wiley & Sons. This is a schematic representation of a burning surface showing the heat and mass transfer processes involved in combustion. Importantly, it shows that in all fire occurrences, heat flux supplied by the flame (QF″) transfers to the fuel surface. This heat transfer then increases the volatility of the fuel, hence adding to the conflagration.
Clearly, therefore, a key aspect of simulating a liquid fuel spill fire is to transmit radiant heat to liquid fuel so as to promote the evaporation of that liquid fuel.
An example of a gas-fuelled fire-fighting simulator is disclosed in U.S. Pat. No. 5,055,050 to Symtron Systems, Inc., which comprises a diffuser such as a pan filled with a bed of dispersive medium such as water or gravel in which a burner system comprising a network of perforated pipes is submerged or buried. The pipes carry pressurised liquefied petroleum gas (LPG)—preferably propane—which is initially in its liquid phase but, with reducing pressure, flashes into the vapour phase within the pipes as it approaches the holes in the pipes. Thus, the pipes contain a mix of vaporising liquid propane and propane vapour. The gas issuing from the pipes diffuses as it rises through the dispersive medium and then burns on the surface of the dispersive medium. Two or more pans can be used side-by-side.
Whilst such use is not specifically disclosed in U.S. Pat. No. 5,055,050, it is well known in the art that the flames can be controlled to respond appropriately to the trainee fire-fighters' actions. For example, the fuel flow rate in different parts of the network of pipes or in different pans can be varied under central control via remote valves. It is also known that the pans can be used beside a prop such as a mock aircraft fuselage to lend further realism to training scenarios.
The simulator arrangement of U.S. Pat. No. 5,055,050 enjoys certain benefits such as low cost and is suitable for many training requirements, but the exposed bed of the dispersive medium causes several problems that the present invention seeks to overcome.
One of the major problems of an exposed bed is that the dispersive medium lacks structural integrity and can bear no significant load. This means that props cannot be supported on the bed and that vehicles cannot drive over the bed without risking fracture of the pipes underneath the surface and so possibly causing a genuine conflagration. It follows that areas of the simulator are artificially off-limits to fire tenders and, for safety reasons, have to be delineated as such with markers or barriers that extend beyond the forbidden area.
Given the reliance upon close approach of fire tenders to aircraft in aviation fire scenarios, it is hugely unrealistic to prevent tenders, in training, accessing areas of the simulator installation that, in an analogous real fire, correspond to areas around an aircraft upon which the tender would advantageously be driven. This problem is particularly acute given that tenders must be driven artificially gently and slowly during training to avoid accidentally driving onto the forbidden areas: in real life, their drivers will approach an accident site at the highest possible speed and brake as hard and late as they can. It is similarly unrealistic to have to place props beside rather on top of the bed, where the simulated fire is raging.
Another disadvantage of the exposed bed of dispersive medium is that props cannot be dragged across the bed if it is desired to rearrange their position: they can only be lifted into place by a crane. This limits the adaptability of the simulator by increasing the cost and timescale of any changes in the orientation or layout of the props, such as may be necessary to track changes in wind direction, if indeed such changes are possible within the confines imposed by the extent of the beds surrounding the location of the prop. Aside from developing fire-fighting skills applicable to different situations, the ability to vary training scenarios is important to maintain the trainees' interest and focus.
There is also the problem that fire-fighter trainees cannot walk safely on the bed of dispersive medium as they fight the simulated fire: even a shallow pan of water is self-evidently unsuitable for access on foot, and the alternative medium of gravel or other particulate refractory material presents a trip hazard that could cause a trainee to stumble into the flames. This drawback further deprives the simulator of realism, because, in real life, fire-fighters will expect to advance on foot as they fight back the flames whereas, when using the simulator, their advance will be limited by the margins of the bed.
Yet another drawback of the exposed bed of dispersive medium is that the medium can be disturbed by the flow of water used by trainee fire-fighters to simulate foam. That flow typically reaches 11,000 litres per minute from each nozzle used to fight the fire. Where the dispersive medium is a particulate medium such as gravel, for example, such a powerful jet of liquid can wash the gravel about within the pan, removing gravel from some parts of the pan and piling it up elsewhere in the pan. At best, this varies the depth of the bed of gravel to the detriment of optimal dispersion and combustion of the fuel rising from the perforated pipes. The behaviour of the simulator may therefore vary unpredictably from one training exercise to the next, unless the gravel is raked back into a level layer between those exercises. At worst, sections of the pipes can be exposed, depriving the out-flowing fuel of any dispersive effect and exposing the pipes to the full radiant heat of combustion.
The present invention seeks to solve these problems and therefore to extend the use of gas-fuelled simulators into other parts of the simulator market, providing a simulator in which the realism of training is as great as can be allowed by the safety of those who operate and train on it.